The present invention relates to a power source control apparatus for a telephone set, for supplying an external power to execute processing when the processing is necessary.
Conventionally, in order to prevent unnecessary power consumption, no power is supplied to a card type public telephone set in a normal state to set it in an inoperative state. At the same time an off-hook operation for making a call is executed or an incoming signal arrives from an office line, a power is supplied from an external power source such as a commercial power source provided independently of a local power source (internal power source) for based on a line current an operation during power failure to activate the telephone set. That is, when the external power is supplied, a control unit in the telephone set is activated to be in an operative state to execute initialization and determines whether the activation condition is an off-hook output or an incoming detection signal. The control unit performs originating call speech processing or incoming call speech processing in accordance with the determination result. When the speech processing is finished, the control unit stops supply of the external power and transits to a standby state.
In a conventional telephone set of this type, supply and holding of the external power are locally executed in accordance with an off-hook output or incoming signal detection independently of the control circuit. After the control circuit finishes speech processing, the holding state of the power supply is released by an output from the control circuit. Therefore, if the control unit does not perform the release operation because it runs away or for some other reasons, the holding state is not released to fail to stop the power supply. As a result, the power is semipermanently, unnecessarily consumed.